Add sugar and stir (with pan still on heat) for a few minutes, until the sugar dissolves.

Remove from heat and stir in buttermilk. Pour into 4 decorative glasses or ramikins and chill until set, 3 - 4 hours.

To make the sauce (remove 2 thin slices from the 'equator' of the orange before peeling if you want a garnish) peel and chop the oranges. Mix the chopped orange with sugar, salt and cinnamon in a saucepan. Use approximately 2 tablespoons of the water to mix with the cornstarch, then stir this mixure and the remaining water into the oranges.

Cook over medium-low heat, stirring constantly, until mixture thickens and begins to look clear. Set aside to cool. Serve on or alongside the panna cotta.